1. Field of the Invention
The present teaching relates to a nonaqueous electrolytic solution secondary battery, and more particularly to a negative electrode material for a nonaqueous electrolytic solution secondary battery. The present application claims priority to Japanese Patent Application No. 2015-222486 filed on Nov. 12, 2015, the entire contents of which are incorporated by reference in the present description.
2. Description of the Related Art
Nonaqueous electrolytic solution secondary batteries represented by lithium ion secondary batteries are low in weight and make it possible to obtain a high energy density, and thus have been widely used as portable power sources for personal computers or portable terminals and also as drive power sources for vehicles.
Meanwhile, nonaqueous electrolytic solution secondary batteries, such as lithium ion secondary batteries, which are used as drive power sources for vehicles need to be charged or discharged at a high current over a short period of time. Therefore, an excellent rapid charge-discharge characteristic (that is, a high-rate characteristic) is required for drive power sources for vehicles.
Furthermore, nonaqueous electrolytic solution secondary batteries, such as lithium ion secondary batteries, which are used as drive power sources for vehicles need to demonstrate continuously stable performance even in repeated charge-discharge cycling in any number of cycles over a long period of time after installation on a vehicle. For this reason, excellent durability (that is, a cycle characteristic) is also required for drive power sources for vehicles.
A variety of approaches have been attempted to improve the aforementioned characteristics. One of them is the improvement of a negative electrode material which is used in the nonaqueous electrolytic solution secondary battery. As an example of such technique, Japanese Patent Application Publication No. 2000-348719 discloses a nonaqueous electrolytic solution secondary battery in which a high-rate characteristic is improved by reducing the internal resistance of a negative electrode by obtaining smooth lithium ion diffusion inside the negative electrode. In the negative electrode of such a nonaqueous electrolytic solution secondary battery, a negative electrode active material layer is formed that includes a negative electrode active material formed of a graphite material and carbon black characterized by a dibutyl phthalate (DBP) absorption amount being equal to or greater than a predetermined value.
Japanese Patent Application Publication No. 2000-348719 indicates that the ability of the negative electrode to retain the nonaqueous electrolytic solution is increased by including such carbon black with a high DBP absorption amount in the negative electrode active material layer within a range from 0.05% by weight (inclusive) to 5% by weight (inclusive), which makes it possible to obtain smooth lithium ion diffusion between the graphite particles which are the positive electrode active material.